Today, the Midwest got a reprieve from this winter's bitter cold. But that long, deep freeze has created so much ice cover on the Great Lakes that it's near record levels. It's also really tempting for many people who want to walk out on the ice.

As NPR's Cheryl Corley reports while that may be fun, it is also dangerous.

CHERYL CORLEY, BYLINE: Along some areas of Chicago's Lakefront, it's been difficult at times this winter to tell exactly where the shoreline ends and Lake Michigan begins.

RON DORNEKER: And when the ice formations are out there, it's gorgeous.

CORLEY: Ron Dorneker, the head of the Chicago Fire department's scuba diving and rescue operations, says it's also very alluring.

DORNEKER: And so, people are walking over the ice and they believe it to be shoreline, but actually it's over open water.

CORLEY: And sometimes they fall through. This past weekend, Chicago police ticketed a family with a young child for walking around mounds of ice and snow about 100 yards from shore.

Jia Wang, an ice climatologist with the Great Lakes Environmental Research Laboratory, says what's building the ice are those persistent blasts of arctic air that's left people shivering.

JIA WANG: The ice cover right nowadays is over 80 percent for the Lake Michigan.

CORLEY: And all the other Great Lakes, except for Lake Ontario, are nearly completely covered with ice. Lake Erie, the shallowest, is the most frozen. Lake's Huron ice cover is so thick, a small plane in trouble used it for a runway this week. And thousands of tourists have been doing the unthinkable: hiking across Lake Superior to check out the amazing Apostle Island sea caves, in Wisconsin that are usually only accessible by kayak or canoe with a guide.

WANG: This is a very historic. It's almost reaching 1979 level.

CORLEY: Researcher Wang says during the brutal winter of 1979, ice cover over the Great Lakes was nearly complete at 94 percent. Twenty years ago, it was 90 percent. Today it's 85 percent. And with temperatures on the rise, the records set earlier could likely remain intact - even though stubborn below freezing temperatures are expected to return.

For some the idea of venturing out on Lake Michigan's snow and ice covered water is simply...

FRANK MARZLOCK: Crazy, because, you know, this is not solid ice.

CORLEY: Frank Marzlock is a retired biology professor.

Still, the beauty of the ice is more than enough to entice others and Fire Chief Dorneker says his crews were called out for two incidents recently, close to where the professor was walking.

DORNEKER: One of them was with a dog that had fallen in. It slipped on the ice and fell in.

CORLEY: The dog's owner went in after the dog. Luckily, a jogger and a cross country snow skier were able to keep both alive until rescue crews arrived.

Ice fisherman Arden Katz says he wouldn't walk out on the ice at Chicago's Lake Shore because the current underneath is pretty strong. But he says the ice where's he's fishing in Montrose harbor is about two feet thick and he couldn't be happier.

ARDEN KATZ: It's the best ice fishing I've had in years, because you can go everywhere and you don't have to worry about falling in, you know, safety-wise. It's been unbelievable.

CORLEY: Kyle and Janine Kostelny say it's pretty astonishing. They walked down a nearby boat ramp, jumped on the ice and started taking a stroll.

KYLE KOSTELNY: Ah, we're just doing it just to say we done it.

JANINE KOSTELNY: Yeah.

KOSTELNY: Yeah.

KOSTELNY: Pretty cool. This is my first time. Forty-seven years old, first time I walked on water.

(LAUGHTER)

CORLEY: Frozen water that is and, dangerous or not, it's likely to be around for a while.